Lesson video

Hi, I'm Mrs. Adcock, and today we are going to be learning about evolution of the Earth's atmosphere.

We're gonna be answering the question, how did the atmosphere change from the early atmosphere to the atmosphere that we have nowadays? Today's lesson outcome is I can describe how Earth's atmosphere developed over billions of years.

Some key words that we will use in today's lesson include volcano, sedimentary rock, photosynthesis, algae, and phytoplankton.

Here you can see those keywords used in a sentence.

So you could pause the video here and either just read through those sentences or you might want to make a note of them, so you can refer back to them later on in the lesson.

Today's lesson is split into two parts.

So the first part is Earth's early atmosphere, and then we're gonna look at changes in the atmosphere.

Right, let's get started on Earth's early atmosphere.

The Earth formed approximately 4.

6 billion years ago, and we can see a picture there of what early Earth might have looked like.

One scientific theory is that for the first billion years, Earth was very hot with intense volcanic activity.

So the Earth was covered in volcanoes over its surface, and the volcanoes released gases.

And it was these gases that formed the Earth's early, the Earth's first atmosphere, and that first atmosphere would've been very different to the atmosphere we have today on Earth.

The Earth's early atmosphere is thought to have contained the following gases, large amounts of carbon dioxide.

And by large amounts, we mean that the early atmosphere is thought to have consisted of at least 90% carbon dioxide, along with some nitrogen, ammonia, methane, and water vapour.

Now if we look at the diagram, we can see these gases being emitted from a volcano.

And when they were emitted, they formed the Earth's early atmosphere.

So CO2, that's carbon dioxide; we've got H2O, which is our water vapour; NH three is ammonia; N2 is nitrogen; and CH4, that's methane.

There may have been little or no oxygen present in the early atmosphere.

Right, time to check for understanding.

Approximately how old is Earth? Is it a, 100 million years; b, 4.

6 billion years; or c, 2.

5 billion years? The correct answer is b.

Well done if you chose b.

The Earth is approximately 4.

6 billion years old.

Which gas was the most dependent in Earth's early atmosphere? Was it a, oxygen; b, methane; or c, carbon dioxide? The correct answer is c.

So well done if you chose c, carbon dioxide was the most abundant gas in Earth's early atmosphere.

Earth's early atmosphere is thought to have been very similar to the atmosphere on Mars and Venus today.

So we've got a table here where we can see the approximate percentage composition of gas in the atmosphere on Mars and on Venus.

And if you have a look, you can see that both Mars and Venus contain a large amount of carbon dioxide.

So they've got 95 and 96% composition of carbon dioxide in the atmosphere.

They then contain some nitrogen, argon, and some other gases, and you can see there that both of them have got very low, so trace amounts of oxygen in the atmosphere.

So could humans survive on Mars and Venus? Although scientists have made predictions about the Earth's early atmosphere, they cannot know for certain what Earth's early atmosphere was like billions of years ago.

Some examples of where they can collect evidence to help them work out what Earth's early atmosphere was like include looking at the gases trapped inside meteorites, the gases released during volcanic eruptions, the Earth's oceans; rocks from Earth and other planets.

And you can see there in the diagram, we've got an picture of an ancient rock sample, and within there are little pores where there's gases trapped and then scientists can study those gases from ancient rocks to try and find more information about what Earth's early atmosphere was like.

So the oldest rocks that have been found on Earth are thought to be 4.

3 billion years old.

Scientists cannot be 100% sure what the atmosphere was like 4.

6 billion years ago.

So we've just looked at how the scientists collect their evidence on the Earth's early atmosphere, but they cannot be 100% sure.

And some of the reasons for this include the rock cycle.

Now that means it's difficult to find rocks from this period.

If we look at the diagram there, this just reminds us that in the rock cycle, any sedimentary rock will eventually become metamorphic rock, that will become igneous rock, and so the cycle continues.

The large timescale.

So we are talking about 4.

6 billion years ago, and that large timescale means evidence is very limited.

And there are no records from this time due to no life on Earth.

So there were no scientists 4.

6 billion years ago making records and recording what the atmosphere was like.

Time for another check.

So is this statement true or false? Scientists have analysed the air trapped in ancient rocks to gather evidence on what Earth's atmosphere was like billions of years ago.

That statement is true.

So well done if you put true.

Now see if you can justify your answer.

Is that statement true? Because a, air samples reveal that the atmosphere contained large amounts of carbon dioxide; or records taken 6 billion years ago reveal that the atmosphere contained low levels of oxygen.

So well done if you put a.

A is the correct answer, air samples reveal that the atmosphere contained large amounts of carbon dioxide.

It couldn't be b because Earth is only 4.

6 billion years old and there weren't any records taken then because there was no life on Earth.

Why can scientists not say for definite what the composition of Earth's early atmosphere was? Is it because a, data records have been lost; b, some ancient rocks have been destroyed by the rock cycle; c, scientists from this period have died; or d, it is too long ago that there are no records? Now it might be just one answer or you might think it's more than one of these answers, so choose any that you think are correct.

So b and d are both correct.

So well done if you have b and d.

Time for us to have a go as a practise task.

The table shows the percentage composition of gases in the atmosphere on Mars and Earth today.

So use the information to describe how the composition of Earth's atmosphere has changed over time.

Remembering the Earth's early atmosphere is thought to have been similar to the atmosphere on Mars today.

The table shows us the approximate percentage composition of gas in the atmosphere, and we can see we've got the levels of carbon dioxide, nitrogen, argon, oxygen, and other gases.

And you've got that information from Mars, which represents Earth's early atmosphere.

And then you've got Earth as it is nowadays.

If you pause the video, have a go at the answering this question and then I'll see you back in a few minutes ready to go over the answer.

Your answer may include the following.

The amount of carbon dioxide in the atmosphere has decreased from more than 90% to only approximately 0.

04%.

The amount of nitrogen in the atmosphere has increased, and this is because nitrogen has been unreactive, so it's released from those volcanoes and slowly built up over time.

The amount of argon in the atmosphere is similar to the levels 4.

6 billion years ago.

There is only 0.

13% oxygen in Mars' atmosphere.

There may have been little or no oxygen present in Earth's early atmosphere and the level of oxygen has increased to approximately 21% today.

Well done if you included many of those points in your answer.

Time for us to move on to the second part of our lesson on changes in the atmosphere.

Scientists can study volcanic eruptions to gather evidence of how historical volcanoes impacted the early atmosphere.

The Hunga Tonga-Hunga Ha'apai volcano erupted in January 2022 and sent a massive plume of water vapour into the atmosphere.

And it was so big that it was seen by astronauts on the International Space Station.

The amount released is estimated to have been enough to fill more than 58,000 Olympic sized swimming pools.

And we've got a photo there showing a volcano releasing water vapour and other gases into the atmosphere.

Water vapour released during volcanic eruptions existed in Earth's early atmosphere also.

So what happened to all this water vapour in the atmosphere? The Earth's surface temperature called over time and when the surface temperature called to less than 100 degrees Celsius, water vapour in the atmosphere condensed to form the oceans.

And there's a diagram there of an ocean.

And just a reminder that our oceans formed when the Earth cold and the water vapour condensed.

Time for a check.

The surface temperature on planet Z is 285 degrees Celsius.

Why does planet Z contain no oceans? Is it a, planet Z does not contain enough water vapour to form an ocean; b, planet Z has volcanic activity which produces water vapour; or c, planet Z is too hot.

Water condenses at 100 degrees Celsius.

The correct answer is c.

So well done if you chose c.

The amount of oxygen gas in the atmosphere has increased.

We can see from the table here that Earth's early atmosphere contained no or very little oxygen, whereas Earth's atmosphere today contains about 21% oxygen gas.

So where did all this oxygen come from? Well, about 3 billion years ago, algae evolved and there's many different theories as to how this algae evolved, and algae are a very diverse range of photosynthetic organisms. The algae evolved and they introduced oxygen into the atmosphere.

And over the next billion years, plants evolved and increased the levels of oxygen in the atmosphere to the level where animals could now evolve and survive on Earth, because obviously the oxygen is essential for animals to be able to respire.

Algae don't have the some of the complex features that plants have, but algae are able to photosynthesize.

The equation for photosynthesis is carbon dioxide and water react together to form glucose and oxygen.

And you can see there we've got this a balanced similar equation for photosynthesis as well.

This process of photosynthesis is essential for releasing oxygen into the atmosphere.

Phytoplankton, including some algae, in the oceans are responsible for about half of all photosynthesis that takes place on planet Earth.

Now these algae can be single celled or they could be multicellular organisms, and they are for all photosynthesizing to release oxygen gas.

Phytoplankton are estimated to have produced 50% of the oxygen in our atmosphere.

Phytoplankton are also essential for animals forming the base of many aquatic food webs, and we can see an example there of a food chain which will be part of a larger food web.

Algae are food for shrimp, who are food for cod, which are food for seals, which are food for polar bears.

Let's check that we've understood.

So a true or false question.

Algae evolved and increased the level of carbon dioxide through photosynthesis.

Is this true or false? So that statement is false.

Can you justify your answer? A, algae evolved and increased the level of carbon dioxide through respiration; or b, algae evolved and increased the level of oxygen through photosynthesis.

Well done if you put b.

Which option correctly shows the equation for photosynthesis? Is photosynthesis a, where carbon oxide and water react to form glucose and oxygen; is it b, glucose and oxygen react to form carbon dioxide and water; or c, fuel and oxygen reacts to form carbon dioxide and water.

Well done if you chose answer a.

Answer a correctly shows the equation for photosynthesis.

The levels of oxygen in the atmosphere we've seen have increased significantly, whereas the levels of carbon dioxide in the atmosphere have decreased significantly over time.

We can see in the table that the Earth's early atmosphere is thought to have contained over 90% carbon dioxide, whereas Earth's atmosphere today contains approximately 0.

04% carbon dioxide.

What happened that led to a decrease in carbon dioxide in the atmosphere? Well, algae and plants we've already seen evolved and they started photosynthesizing.

And as they photosynthesize, they've removed carbon dioxide from the atmosphere and released oxygen into the atmosphere.

What else might have led to a decreased amount of carbon dioxide, so CO2, in the atmosphere? Number one, carbon dioxide is soluble and dissolved in the oceans when they formed.

When the water vapour condensed to form the oceans, some of the carbon dioxide from the atmosphere dissolved in the oceans.

Number two, carbon dioxide in the oceans reacted to form insoluble carbonate compounds, which can be used to make shells and bones.

So the carbon dioxide from the atmosphere is now locked up in shells and bones.

When marine organisms die, these shells and bones settle at the bottom of the ocean where over millions of years, they form sedimentary rocks.

The carbon dioxide has been removed from the atmosphere and become locked up in rocks.

Number three, marine plants and algae die along with the animals which consumed them.

So all the animals along those food chains and within the food web all die.

The dead remains become buried in mud and rock forming fossil fuels over millions of years.

So the carbon dioxide from the atmosphere has become locked up again as carbon in fossil fuels.

Carbon can take 100 to 200 million years to move between rocks, soil, oceans, and the atmosphere in a slow cycle.

So any carbon dioxide removed from the atmosphere, it'll take a long time for it to be released back into the atmosphere again.

Time for a check for understanding.

The percentage of carbon dioxide in the atmosphere today is higher than in Earth's early atmosphere, lower than in Earth's early atmosphere, or the same as in Earth's early atmosphere.

The correct answer is b.

The percentage of carbon dioxide in the atmosphere today is lower than in Earth's early atmosphere.

So well done if you got that one correct.

Our final practise task in today's lesson is to explain why the levels of carbon dioxide and oxygen have changed from Earth's early atmosphere to Earth's atmosphere today.

In your answer, make sure to include the equation for photosynthesis.

If you wanna pause the video here, have a go at answering this question, and I'll see you back in a moment to go over the answer.

The first part of your answer may include, oxygen levels have increased as algae implants evolved and photosynthesize releasing oxygen into the atmosphere.

And this would've been a good time to include the equation for photosynthesis, which is carbon dioxide plus water react to produce glucose plus oxygen.

The second part of your answer may include algae implants photosynthesizing reduced the amount of carbon dioxide in the atmosphere.

Carbon dioxide was also removed from the atmosphere when it dissolved in the oceans.

It formed carbonates, which over time became part of sedimentary rocks.

Marine plants and animals died and locked the carbon in fossil fuels formed over millions of years.

Well done if you included lots of those details in your answer.

Let's summarise what we've in today's lesson.

Early volcanic activity is thought to have made an atmosphere of carbon dioxide and nitrogen billions of years ago.

Carbon dioxide can dissolve in oceans and form carbonates, which over millions of years form sedimentary rock.

The amount of carbon dioxide was reduced by the formation of sedimentary rocks and photosynthesis by algae and plants.

Algae plants produced the oxygen that is now in the atmosphere by the process of photosynthesis.

Phytoplankton, including algae, in the oceans are responsible for about half of all photosynthesis that takes place today.

Well done today.

You've worked really hard and we've learned lots of key facts about how the atmosphere has changed from Earth's early atmosphere to the atmosphere on Earth today.

I hope you've enjoyed your learning and I look forward to seeing you in the next lesson.